4:1 Unbalance to Unbalance Coaxial Transformer

This is my first time to implement the 4:1 unbalance to unbalance coaxial transformer to match the input and output impedance of an rf power transistor. My prototype rf amplifier originally had a lumped LC network in both input and output sections and only have +/- 3MHz of bandwidth but after the addition of 4:1 coaxial transformer, the bandwidth has now increased to +/- 6MHz from the center tuning frequency of the amplifier.
The coaxial transformer is about 1/16th wavelength long from the highest frequency in which the amplifier will work and should have 25 ohm of characteristic impedance. In my prototype amp it uses a pair of RG-178 cable paralleled to arrive at the 25 ohm requirement.

This is the simplified diagram when looking at the transformer however, the characteristic impedance of the coaxial cable also plays an important role in the impedance ratio. For a 50 ohm to 12.5 ohm transformation, it calls for a 25 ohm cable but since I don't have this kind, I simply paralleled two RG178, a 50 ohm cable.

The schematic diagram of my prototype amp tells that aside from the 4:1 coaxial transformer, LC network was still employed to further matched the impedance of the base and collector of the power rf transistor. The only limiting factor that prevents the amplifier for a broadband operation is the LC network!

My prototype amp after the inclusion of the 4:1 coaxial transformer. I might replace the old PCB to facilitate the addition of the two coaxial transformer. ---73 de du1vss